<s>
ARexx	B-Operating_System
is	O
an	O
implementation	O
of	O
the	O
Rexx	B-Language
language	O
for	O
the	O
Amiga	B-Device
,	O
written	O
in	O
1987	O
by	O
William	O
S	O
.	O
Hawes	O
,	O
with	O
a	O
number	O
of	O
Amiga-specific	O
features	O
beyond	O
standard	O
REXX	B-Language
facilities	O
.	O
</s>
<s>
Like	O
most	O
REXX	B-Language
implementations	O
,	O
ARexx	B-Operating_System
is	O
an	O
interpreted	B-Application
language	I-Application
.	O
</s>
<s>
Programs	O
written	O
for	O
ARexx	B-Operating_System
are	O
called	O
"	O
scripts	B-Language
"	O
,	O
or	O
"	O
macros	O
"	O
;	O
several	O
programs	O
offer	O
the	O
ability	O
to	O
run	O
ARexx	B-Operating_System
scripts	B-Language
in	O
their	O
main	O
interface	O
as	O
macros	O
.	O
</s>
<s>
ARexx	B-Operating_System
can	O
easily	O
communicate	O
with	O
third-party	O
software	O
that	O
implements	O
an	O
"	O
ARexx	B-Operating_System
port	O
"	O
.	O
</s>
<s>
Any	O
Amiga	B-Device
application	O
or	O
script	O
can	O
define	O
a	O
set	O
of	O
commands	O
and	O
functions	O
for	O
ARexx	B-Operating_System
to	O
address	O
,	O
thus	O
making	O
the	O
capabilities	O
of	O
the	O
software	O
available	O
to	O
the	O
scripts	B-Language
written	O
in	O
ARexx	B-Operating_System
.	O
</s>
<s>
ARexx	B-Operating_System
can	O
direct	O
commands	O
and	O
functions	O
to	O
several	O
applications	O
from	O
the	O
same	O
script	O
,	O
thus	O
offering	O
the	O
opportunity	O
to	O
mix	O
and	O
match	O
functions	O
from	O
the	O
different	O
programs	O
.	O
</s>
<s>
For	O
example	O
,	O
an	O
ARexx	B-Operating_System
script	O
could	O
extract	O
data	O
from	O
a	O
database	O
,	O
insert	O
the	O
data	O
into	O
a	O
spreadsheet	B-Application
to	O
perform	O
calculations	O
on	O
it	O
,	O
then	O
insert	O
tables	O
and	O
charts	O
based	O
on	O
the	O
results	O
into	O
a	O
word	B-General_Concept
processor	I-General_Concept
document	O
.	O
</s>
<s>
ARexx	B-Operating_System
was	O
first	O
created	O
in	O
1987	O
,	O
developed	O
for	O
the	O
Amiga	B-Device
by	O
William	O
S	O
.	O
Hawes	O
.	O
</s>
<s>
It	O
is	O
based	O
on	O
the	O
REXX	B-Language
language	O
described	O
by	O
Mike	O
Cowlishaw	O
in	O
the	O
book	O
The	O
REXX	B-Language
Language	O
:	O
A	O
Practical	O
Approach	O
to	O
Programming	O
.	O
</s>
<s>
ARexx	B-Operating_System
was	O
included	O
by	O
Commodore	O
with	O
AmigaOS	B-Application
2.0	O
in	O
1990	O
,	O
and	O
has	O
been	O
included	O
with	O
all	O
subsequent	O
AmigaOS	B-Application
releases	O
.	O
</s>
<s>
This	O
later	O
version	O
of	O
ARexx	B-Operating_System
follows	O
the	O
official	O
REXX	B-Language
language	O
closely	O
;	O
Hawes	O
was	O
later	O
involved	O
in	O
drafting	O
the	O
ANSI	O
standard	O
for	O
REXX	B-Language
.	O
</s>
<s>
ARexx	B-Operating_System
is	O
written	O
in	O
68000	B-Device
Assembly	O
,	O
and	O
cannot	O
therefore	O
function	O
at	O
full	O
speed	O
with	O
new	O
PPC	O
CPUs	O
,	O
a	O
version	O
of	O
ARexx	B-Operating_System
has	O
not	O
been	O
rewritten	O
for	O
them	O
and	O
is	O
still	O
missing	O
from	O
MorphOS	B-Operating_System
3.0	O
.	O
</s>
<s>
William	O
Hawes	O
is	O
no	O
longer	O
involved	O
in	O
development	O
of	O
Amiga	B-Device
programs	O
and	O
no	O
other	O
Amiga-related	O
firm	O
is	O
financing	O
new	O
versions	O
of	O
ARexx	B-Operating_System
.	O
</s>
<s>
Notwithstanding	O
this	O
fact	O
,	O
the	O
existing	O
version	O
of	O
ARexx	B-Operating_System
continues	O
to	O
be	O
used	O
,	O
although	O
it	O
is	O
not	O
distributed	O
with	O
MorphOS	B-Operating_System
.	O
</s>
<s>
in	O
assembly-language	O
using	O
the	O
Metacomco	B-Device
assembler	O
.	O
</s>
<s>
was	O
created	O
using	O
the	O
TxEd	O
editor	O
,	O
and	O
was	O
set	O
in	O
TeX	B-Application
using	O
AmigaTeX	B-Device
.	O
</s>
<s>
ARexx	B-Operating_System
is	O
a	O
programming	O
language	O
that	O
can	O
communicate	O
with	O
other	O
applications	O
.	O
</s>
<s>
Using	O
ARexx	B-Operating_System
,	O
for	O
example	O
,	O
one	O
could	O
request	O
data	O
from	O
a	O
database	O
application	O
and	O
send	O
it	O
to	O
a	O
spreadsheet	B-Application
application	O
.	O
</s>
<s>
To	O
support	O
this	O
facility	O
,	O
an	O
application	O
must	O
be	O
"	O
ARexx	B-Operating_System
compatible	O
"	O
by	O
being	O
able	O
to	O
receive	O
commands	O
from	O
ARexx	B-Operating_System
and	O
execute	O
them	O
.	O
</s>
<s>
A	O
database	O
program	O
might	O
have	O
commands	O
to	O
search	O
for	O
,	O
retrieve	O
,	O
and	O
save	O
data	O
the	O
MicroFiche	O
Filer	O
database	O
has	O
an	O
extensive	O
ARexx	B-Operating_System
command	B-Application
set	O
.	O
</s>
<s>
A	O
text	O
editor	O
might	O
have	O
ARexx	B-Operating_System
commands	O
corresponding	O
to	O
its	O
editing	O
command	B-Application
set	O
the	O
Textra	O
editor	O
supplied	O
with	O
JForth	O
can	O
be	O
used	O
to	O
provide	O
an	O
integrated	O
programming	O
environment	O
.	O
</s>
<s>
The	O
AmigaVision	O
multimedia	O
presentation	O
program	O
also	O
has	O
ARexx	B-Operating_System
port	O
built	O
in	O
and	O
can	O
control	O
other	O
programs	O
using	O
ARexx	B-Operating_System
.	O
</s>
<s>
ARexx	B-Operating_System
can	O
increase	O
the	O
power	O
of	O
a	O
computer	O
by	O
combining	O
the	O
capabilities	O
of	O
various	O
programs	O
.	O
</s>
<s>
Because	O
of	O
the	O
popularity	O
of	O
a	O
stand-alone	O
ARexx	B-Operating_System
package	O
,	O
Commodore	O
included	O
it	O
with	O
Release	O
2	O
of	O
AmigaDOS	B-Operating_System
.	O
</s>
<s>
Like	O
all	O
REXX	B-Language
implementations	O
,	O
ARexx	B-Operating_System
uses	O
typeless	O
data	O
representation	O
.	O
</s>
<s>
In	O
contrast	O
,	O
REXX	B-Language
systems	O
treat	O
all	O
data	O
as	O
strings	O
of	O
characters	O
,	O
making	O
it	O
simpler	O
to	O
write	O
expressions	O
and	O
algorithms	O
.	O
</s>
<s>
ARexx	B-Operating_System
scripts	B-Language
benefit	O
from	O
an	O
error	O
handling	O
system	O
which	O
monitors	O
execution	O
and	O
responds	O
accordingly	O
.	O
</s>
<s>
The	O
ARexx	B-Operating_System
command	B-Application
set	O
is	O
simple	O
,	O
but	O
in	O
addition	O
to	O
the	O
commands	O
there	O
are	O
the	O
functions	O
of	O
its	O
Amiga	B-Device
reference	O
library	O
(	O
rexxsyslib.library	O
)	O
.	O
</s>
<s>
ARexx	B-Operating_System
scripts	B-Language
can	O
also	O
be	O
invoked	O
as	O
functions	O
from	O
other	O
ARexx	B-Operating_System
scripts	B-Language
.	O
</s>
<s>
Any	O
Amiga	B-Device
program	O
which	O
has	O
an	O
ARexx	B-Operating_System
port	O
built	O
in	O
can	O
share	O
its	O
functions	O
with	O
ARexx	B-Operating_System
scripts	B-Language
.	O
</s>
<s>
If	O
end	O
user	O
is	O
using	O
a	O
program	O
which	O
builds	O
animations	O
by	O
joining	O
various	O
bitmap	O
image	O
files	O
but	O
which	O
lacks	O
image	O
processing	O
capabilities	O
,	O
he	O
could	O
write	O
an	O
ARexx	B-Operating_System
script	O
which	O
performs	O
these	O
actions	O
:	O
</s>
<s>
EqFiles.rexx	O
is	O
a	O
well-known	O
example	O
of	O
a	O
simple	O
ARexx	B-Operating_System
script	O
written	O
to	O
automate	O
repetitive	O
and	O
boring	O
procedures	O
.	O
</s>
<s>
One	O
of	O
the	O
main	O
features	O
of	O
ARexx	B-Operating_System
is	O
the	O
fact	O
it	O
could	O
expand	O
the	O
capabilities	O
of	O
the	O
AmigaOS	B-Application
by	O
adding	O
some	O
procedures	O
the	O
OS	O
lacked	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
simple	O
ARexx	B-Operating_System
program	O
could	O
be	O
written	O
to	O
print	O
a	O
warning	O
message	O
on	O
the	O
screen	O
of	O
the	O
monitor	O
,	O
or	O
play	O
an	O
audio	O
alert	O
signal	O
if	O
a	O
certain	O
Amiga	B-Device
program	O
stops	O
,	O
faults	O
or	O
has	O
finished	O
its	O
scheduled	O
job	O
.	O
</s>
<s>
The	O
following	O
script	O
is	O
a	O
minimal	O
ARexx	B-Operating_System
script	O
that	O
displays	O
warnings	O
depending	O
on	O
events	O
that	O
take	O
place	O
.	O
</s>
